There is known a casing of a vehicular power transmitting device, which is provided with a breather plug which is held in communication with a communication hole formed in the casing and through which an inside space within the casing is open to an outside atmosphere outside the casing. JP2007-64425A discloses an example of such a casing of the vehicular power transmitting device. In the casing disclosed in this publication, the breather plug is provided with a pressure adjusting filter disposed within a passage formed therethrough, so that the breather plug permits only the air to flow through the passage, without flows of oily substances and other foreign matters through the passage. JP2-113072U, JP62-158251U and WO2011/024670 disclose similar prior art breather plugs of the type as described above.
By the way, the breather plug disclosed in JP2007-64425A is screwed to the casing, for preventing removal of the breather plug from the casing. Accordingly, the casing is required to have a threaded portion, so that the threaded portion is required to have a relatively large wall thickness. JP2-113072U discloses an example of a breather plug formed with a removal preventive flange for preventing removal of the breather plug from the casing. This type of breather plug having the integrally formed removal preventive flange has a problem that its length tends to be relatively large.